News that a former adviser to the committee investigating the Jan. 6, 2021, insurrection is publishing a book billed as a “behind-the-scenes” look at the committee’s work came as a shock to most lawmakers and committee staff when it was announced.

Denver Riggleman, a former Republican congressman, is set to publish “The Breach” on Tuesday, one day before the final public hearing of the Jan. 6 panel, which has gone to extraordinary lengths to prevent unauthorized leaks, as well as keep its sources and methods of investigation under wraps.